Diagnoses Amazon S3 Access Denied errors through a thirteen-category diagnostic tree: explicit deny in bucket policy overriding an IAM allow, object ownership mismatch (bucket owner vs uploader), bucket owner enforcement (RequestAccount condition), KMS key policy missing kms:DecryptObject grant, VPC endpoint policy restricting S3 actions, presigned URL expiry or signature mismatch, ACL vs bucket policy conflict, Block Public Access settings, Object Lock retention preventing overwrite or delete, cross-account access requiring both bucket policy and IAM permission, STS assumed-role permission boundary narrowing effective permissions, Service Control Policy denying S3 at the…
